1. Field of the Invention
This invention relates to an ultrasonic diagnostic apparatus, more particularly to an improved ultrasonic diagnostic apparatus which is capable of accurately displaying the velocity distribution of movement of moving members within a living organism.
2. Description of the Prior Art
The ultrasonic pulse-Doppler method has been practically applied to the measurement of the velocity of movement of a body organ such as the heart, of blood flowing in the blood vessels or of other body fluids. The conventional apparatus for applying this method electrically detects the velocity of movement from the frequency shift of an echo reflected from the moving members within the living body but is capable of detecting the velocity of movement only at a specific point at a prescribed depth within the organism. Therefore, in order to obtain the velocity distribution of, for example, flowing blood over a wide target region, it is necessary to repeat the process of sending and receiving ultrasonic pulses many times for many different target points and then to obtain the distribution by synthesizing the results obtained. The process is thus very time consuming. As a consequence, the measurement of the velocity distribution by this method cannot closely follow the changes in the moving members of the organism and, in particular, it is impossible to realize real-time observation of the changes in the blood flow condition caused by pulsation.
As an improved ultrasonic pulse-Doppler apparatus there has been proposed one provided with a plurality of channels so as to make it possible to obtain information on the velocity distribution of flowing blood over a desired region in a single measurement. However, since this improved apparatus, like conventional Doppler apparatuses, has only a narrow band width (usually of only several kHz), it is not capable of collecting Doppler information rapidly, making it difficult to observe the changes in the blood flow condition in B-mode scanning. Also, as it must be provided with many channels, it has the drawbacks of being bulky and costly.